Day 5 Notes – 11.2 Populations, Samples, Hypothesis

Part 1: Populations Vs. Samples

Statistics is: ________________________________________________________________________________________________________

POPULATION:

SAMPLE:

CENSUS:

RANDOM SAMPLE: Why would we use a random sample instead of obtaining all of the population data?

Example: In the United States, a survey of 2184 adults ages 18 and

over found that 1328 of them own at least one pet.

Part 2: Parameter VS. Statistic

PARAMETER: STATISTIC:

HYPOTHESIS:

A drug company claims that patients using its weight-loss drug lose an average of 24

pounds in the first three months.

A die is fair

The percentage of people who like chocolate is 80%.

Part 3: Sampling Types

A sample is used to collect data and make inferences about a population.

1. Random Sample: Every member of the population has an equal likelihood of being selected and the

selection of the sample is made by chance.

2. Systematic Sample: A rule is used to select members of a population.

3. Stratified (Random) Sample: A population is divided into many smaller, homogeneous groups

(called strata) and then a random sample is selected from each stratum.

4. Cluster Sample: A population is divided into many smaller, heterogeneous groups (called clusters)

and everyone within one or more clusters is sampled.

5. Self-Selected Sample: Members of the population can volunteer to be in the sample.

6. Convenience sample: Only members of a population who are easy to reach are selected.

(See Powerpoint)

Reflect: A sample of 200 students be taken from the population of current students at Hinsdale Central

Why could the following allow for more bias:

Self-Selected: Convenience:

Part 4: Bias in Sampling

Bias is: _______________________________________________________________________________________________________________

________________________________________________________________________________________________________________________

Undercoverage: Sample does not include a certain part of the population Nonresponse Bias: bias that results when respondents differ in meaningful ways from nonrespondents. (Nonresponse is often problem with mail surveys, where the response rate can be very low.)

Voluntary Bias: occurs when sample members are self-selected volunteers. Survey includes mostly people who are passionate/have strong options on the matter

Part 5: Bias in Survey Questions

1. Leading questions: Subtly directs respondents toward a particular answer

(Now that you've seen how you can save time, would you buy our product?) 2. Loaded Questions – Include connotations that predispose a respondent to think a certain way.

Survey may use strong words (positive or negative) which carry opinion/judgment.

(Should Americans buy imported automobiles that take away American Jobs?)

3. Double-barreled questions: cover more than one topic.

(When was the last time you upgraded your computer and printer?)

4. Using double negatives

(Please tell me whether or not you agree or disagree with this statement. Graduate teaching assistants should not be required to help students outside of class.)

5. Not using mutually exclusive categories What is your current age?

10 or less 10 to 20

20 to 30

30 or greater

Part 6: Bias in Survey Questions

There are many types of ways to collect data. The most popular are…

1. Experiments and Clinical Trials– impose treatment on individuals in order to collect data on their response

to the treatment. People are put into different groups and the groups are controlled by the researcher.

2. Observation study – directly observing individuals and variables observed are measured WITHOUT

controlling the individuals or the environment.

3. Survey – solicits information from people. Every member of the sample is asked one or more questions.

4. Simulation – uses a model to reproduce the conditions of a situation or process where it might be impractical

or dangerous to create in real life.

FYI, - Do you know what a survey is called that is taken from an entire population?

How often is this done???

Day 5 – Homework (11.3) – Collecting Data

Determine whether the data is collected from a population or a sample. Explain your reasoning.

1) The address of every student in the school.

2) A survey of 80 people who access a website.

3) The GPA of high school students in the United States.

4) The color of every third car that passes your house.

5) A survey of 100 fans at the football game with 1800 spectators.

Part II Identify the population and the sample. Explain your reasoning.

6) In an office building, a survey of 648 employees found that 147 of them ride the subway to work each

day.

7) In Florida, a survey of 2500 homeowners found that 1145 of them have switched their homeowner’s

insurance policy to a different company within the last 3 years.

8) In a school district, a survey of 1,300 high school students found that 1,001 of them like the new healthy

food choices in the cafeteria.

Part III Determine whether the numerical value is a parameter or a statistic. Explain your reasoning.

9) Thirty four percent of the surveyed hockey players first played hockey before their 10th birthday.

10) Eighty-two percent of all the tickets sold were for the Saturday matinee.

11) Seventy-three percent of all of the students in a school would prefer to have school dances on a

Saturday.

12) A survey of U.S. adults found that 10% believe a cleaning product they use is not safe for the environment.

Name the type of sample described.

13. The owners of a chain of 260 retail stores want to assess employee job satisfaction. Employees from 12 stores near

the headquarters are surveyed.

14. The owner of a community pool wants to ask patrons whether they think the water should be warmer. Patrons are

divided into four age groups, and a sample is randomly surveyed from each age group.

15. A taxicab company wants to know whether its customers are satisfied with the service. Drivers survey every tenth

customer during the day.

Determine the type of sample and explain if it is bias or not.

16. A town council wants to know whether residents support having an off-leash area for dogs in the town park. Eighty

dog owners are surveyed at the park.

17. A writer at Sports Illustrated wants to determine whether baseball coaches think wooden bats should be

mandatory in collegiate baseball. The sportswriter divides the colleges by division and then selects a random sample

from each division.

18. The city of Clarendon hills puts a poster up in its town square asking people to take an online survey about

restaurant options in the town.

19. Marquette University wants to conduct a survey of 5,000 alumni. Describe a method of surveying the alumni using

a random sample.

20. Go online and look up the Literary Digest Poll. Please tell what the survey was for and why it failed.

Identify the method of data collection

21. A researcher uses technology to estimate the damage that will be done if a volcano erupts.

22. The owner of Tally’s asks the customers on a Saturday night whether they are satisfied with the quality of their

meal.

23. A researcher places bacteria samples in two different climates. The researcher then measures the bacteria growth

in each sample after 3 days.

Determine whether the survey question may be biased. Explain your reasoning.

24. A police officer asks mall visitors, “Do you wear your seat belt regularly?”

25. Do you favor government funding to help prevent acid rain??

26. Do you agree that the budget of our city should be cut??

27. Please rate your manager on each of the following descriptive scales. Place a checkmark on the space between

each pair of words that best indicates your opinion:

Sociable 1 2 3 4 5 Unsociable

Kind 1 2 3 4 5 Cruel

Hard 1 2 3 4 5 Soft

Successful 1 2 3 4 5 Unsuccessful

Wise 1 2 3 4 5 Foolish

Weak 1 2 3 4 5 Strong